I've always hated the term "cover letter." It implies that the letter you send out to accompany your résumé, the opening shot in your job-hunt campaign, is merely "decoration" for your résumé. A good cover letter does far more than just cover: It engages the reader and makes her want to explore your job qualifications more fully. A good cover letter also highlights your qualifications, guides the reader through the most important parts of your work history, and demonstrates your flawless command of the English language. That's a lot to cover in only three paragraphs!
Don't be daunted. Writing a good cover letter boils down to making a decent presentation of your experience with the employer's needs foremost in mind. This point is extremely important. If you do not have a good understanding of the requirements of the position and the nature of the work involved, how will you be able to answer the needs of the employer? Writing a good cover letter, just like preparing a winning résumé, requires research into the organization you are approaching.
I have distilled eons of wisdom about cover letters into a list of 10 commandments (well, commandments is a little strong; how about recommendations?) that you should bear in mind while preparing your letters. Even if you have already written your cover letter, you may want to use this list as a check on your product.
This may seem obvious, but you must be specific from the outset about why you are sending someone your résumé. Are you applying for an advertised position or just a potential opening? If it is a specific opening, where did you learn about it? You would be surprised how many people fail to mention the specific job to which they are applying. For big companies that are advertising many positions, your lack of specificity may land your résumé in the recycle bin. Even for small operations, it is important to explain how you heard about the job.
Most mediocre cover letters are not specific. They cite items in the résumé but they fail to make the connection to the job that is being advertised. Sure, it's a great thing that you have worked for a summer doing data reduction, but what if they are most concerned about project management experience? You're hosed! You have to show them how your background and experience fit the job they are advertising. At the bare minimum, you should have the job advertisement in front of you as you are writing. But you will be further ahead if you've actually done some research on the company, or better yet, have talked to the people who are advertising the opening.
The best way to prove that you fit is to cite examples in your past work history where you tackled similar job duties or occupied a similar position. Do not assume that they will pick these details out of your résumé, especially as the average employer spends only 20 seconds scanning through a résumé. For example, if you are applying to work in an aeronautical engineering company doing product development, you want to note any specific experience involving the development of a device or experiment rather than just citing your years of experimental work for your Ph.D. Citing specific examples and quantifying them where possible is the best way of convincing a stranger that you've got what it takes to get the job done.
Read the job description and other materials carefully. One way to make your background and experience a better fit is to use the same phrases and descriptors that they use in the job advertisement. This is an important aspect of "speaking the same language" as the employer. If you use the same terms, you will make a more effective connection between your experience and their needs.
Directing cover letters to nameless human resources personnel is like asking the crocodiles in the moat to lower the drawbridge! HR people are best at scanning résumés and matching job descriptors with items on people's résumés. They are not very good at figuring out how someone with an unusual background (like having a Ph.D.) will fit into a particular position. That decision is left with the hiring manager. In some cases, especially with large companies, it is impossible to do a complete end run around the HR department. In those cases, the best you can do is send a duplicate cover letter and résumé to the person who is actually making the hiring decision. Don't know who that is? Call and find out!
It doesn't take clairvoyance to guess what questions might be uppermost in the mind of someone who reads your cover letter. If you are applying for a job for which a Ph.D. is not required, one obvious question is: "Why is a Ph.D. applying for this job?" Another question might be: "Is this person overqualified?" It is important to anticipate these questions and allay any concerns in your cover letter. It is important to show how your experience as a scientist would be an asset in a wide variety of positions.
One-page cover letters are a rule unless you have some specific reasons to make them longer (for example, if the job description or advertisement asks for answers to questions or for more information). In fact, three paragraphs should be sufficient. If your letter is any longer, you'd better have a good reason. Here is a suggested general structure:
A sad story about how you have been searching for a job for the last 4 years may be sincere and truthful, but it rarely makes a good impression. A good cover letter should project an image of confidence and professionalism. Save the confessions until after you get the job.
Your cover letter should be an example of your best written communication. Therefore, it should be self-evident that the writing should be clear, distinctive, and devoid of clichés. But many people can't help but insert some stock cover letter phrases such as: "Enclosed please find ..." or "Thank you for your consideration." These phrases are so routine in cover letters! Say those things differently! Be unique! Show some flair!
Some companies are using electronic résumé tracking for all their applicants. Many times they don't bother scanning in the cover letter at all and simply throw it away. Spending a great deal of time on a cover letter in these cases is a waste. It would be far wiser to find out the name of the person who is the hiring manager and contact them separately in a letter, either with or without a copy of your résumé. The personal contact and attention to detail that a separate letter represents is important.
There is a final transcendent rule for sending out your job materials: following up! You would be surprised how many people simply mail off their materials and never bother to check back with the employer to see if they have actually arrived. Following up with a phone call a week or so after mailing your job materials does two things. First, it ensures that your letter arrived. More importantly, it demonstrates that you are able to follow through and shows that you are genuinely interested in the job. I have heard from several hiring managers who have been impressed by such a simple act.